When designing a multi-layer PCB, you need to pay attention to a basic situation, that is, how many wiring layers, ground planes, and power planes are needed to achieve the required functions of the circuit. The establishment of the number of wiring layers, ground planes, and power planes of the multi-layer PCB is related to the basic functions of the circuit, signal integrity, EMI, EMC, manufacturing costs, etc.

　　Compared with most designs, there are many conflicting requirements for key factors such as PCB performance requirements, cost, manufacturing technology and system complexity. The stacking design of multi-layer PCB circuit boards is generally determined by compromise after considering key factors in various aspects. High-speed digital circuits and radio frequency circuits generally adopt multi-layer board design.

　　1. Layering

　　In a multilayer PCB, there are usually signal, power and ground planes. The power plane and ground plane are generally undivided physical planes. They provide a good low-impedance current return path for the current of the adjacent signal traces.

　　Most of the signal layers are between these power or ground reference plane layers, forming symmetrical strip lines or asymmetrical strip lines. The top and bottom layers of multi-layer PCB circuit boards are generally used to prevent components and a small amount of routing. The routing of this type of signal is not required to be too long to reduce the direct radiation caused by the routing.

　　2. Determine the single power supply reference plane

　　Safe use of decoupling capacitors is a critical measure to deal with power integrity. Decoupling capacitors can only be placed on the top and bottom layers of multi-layer PCB circuit boards.

　　The routing, pads, and vias of the decoupling capacitors will seriously affect the effect of the decoupling capacitors. Therefore, the routing of the decoupling capacitors must be fully considered during design. They should be as short and wide as possible, and the wires connected to the vias should also be as short as possible.

　　3. Determine the multi-power reference plane

　　The multi-power reference plane will be divided into several physical areas with different voltages. If the signal layer is adjacent to the multi-power layer, the signal current on the signal layer nearby may encounter an unsatisfactory return path, causing gaps in the return path.

　　Relative to high-speed digital signals, these unreasonable return path designs may cause serious problems, so high-speed digital signal wiring needs to be away from multiple power reference planes.

　　4. Identify multiple ground reference planes

　　Numerous ground reference planes create a good low impedance current return path, which can greatly reduce common mode EMI.

　　The ground plane and the power plane need to be tightly coupled, and the signal layer should also be tightly coupled with the adjacent reference plane. Reduce the dielectric thickness between layers to achieve this goal.

　　5. Reasonable design of wiring combination

　　The two levels that a signal path jumps over are called a wiring combination. The most suitable wiring combination design is to avoid the return current from flowing from one reference plane to another reference plane as much as possible; instead, it stays from one point (plane) of a reference plane to another point (plane).

　　In order to achieve complex wiring, the inter-layer transition of the routing is inevitable. When transitioning between signal layers, it is necessary to ensure that the return current can flow smoothly from one reference plane to another.

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